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package javax.naming.spi;

import java.util.Hashtable;

import javax.naming.*;

/**
 * This interface represents a factory for creating an object.
 * <p>
 * The JNDI framework allows for object implementations to
 * be loaded in dynamically via <em>object factories</em>.
 * For example, when looking up a printer bound in the name space,
 * if the print service binds printer names to References, the printer
 * Reference could be used to create a printer object, so that
 * the caller of lookup can directly operate on the printer object
 * after the lookup.
 * <p>An <tt>ObjectFactory</tt> is responsible
 * for creating objects of a specific type.  In the above example,
 * you may have a PrinterObjectFactory for creating Printer objects.
 * <p>
 * An object factory must implement the <tt>ObjectFactory</tt> interface.
 * In addition, the factory class must be public and must have a
 * public constructor that accepts no parameters.
 * <p>
 * The <tt>getObjectInstance()</tt> method of an object factory may
 * be invoked multiple times, possibly using different parameters.
 * The implementation is thread-safe.
 * <p>
 * The mention of URL in the documentation for this class refers to
 * a URL string as defined by RFC 1738 and its related RFCs. It is
 * any string that conforms to the syntax described therein, and
 * may not always have corresponding support in the java.net.URL
 * class or Web browsers.
 *
 * @author Rosanna Lee
 * @author Scott Seligman
 * @see NamingManager#getObjectInstance
 * @see NamingManager#getURLContext
 * @see ObjectFactoryBuilder
 * @see StateFactory
 * @since 1.3
 */

public interface ObjectFactory {

  /**
   * Creates an object using the location or reference information
   * specified.
   * <p>
   * Special requirements of this object are supplied
   * using <code>environment</code>.
   * An example of such an environment property is user identity
   * information.
   * <p>
   * <tt>NamingManager.getObjectInstance()</tt>
   * successively loads in object factories and invokes this method
   * on them until one produces a non-null answer.  When an exception
   * is thrown by an object factory, the exception is passed on to the caller
   * of <tt>NamingManager.getObjectInstance()</tt>
   * (and no search is made for other factories
   * that may produce a non-null answer).
   * An object factory should only throw an exception if it is sure that
   * it is the only intended factory and that no other object factories
   * should be tried.
   * If this factory cannot create an object using the arguments supplied,
   * it should return null.
   * <p>
   * A <em>URL context factory</em> is a special ObjectFactory that
   * creates contexts for resolving URLs or objects whose locations
   * are specified by URLs.  The <tt>getObjectInstance()</tt> method
   * of a URL context factory will obey the following rules.
   * <ol>
   * <li>If <code>obj</code> is null, create a context for resolving URLs of the
   * scheme associated with this factory. The resulting context is not tied
   * to a specific URL:  it is able to handle arbitrary URLs with this factory's
   * scheme id.  For example, invoking <tt>getObjectInstance()</tt> with
   * <code>obj</code> set to null on an LDAP URL context factory would return a
   * context that can resolve LDAP URLs
   * such as "ldap://ldap.wiz.com/o=wiz,c=us" and
   * "ldap://ldap.umich.edu/o=umich,c=us".
   * <li>
   * If <code>obj</code> is a URL string, create an object (typically a context)
   * identified by the URL.  For example, suppose this is an LDAP URL context
   * factory.  If <code>obj</code> is "ldap://ldap.wiz.com/o=wiz,c=us",
   * getObjectInstance() would return the context named by the distinguished
   * name "o=wiz, c=us" at the LDAP server ldap.wiz.com.  This context can
   * then be used to resolve LDAP names (such as "cn=George")
   * relative to that context.
   * <li>
   * If <code>obj</code> is an array of URL strings, the assumption is that the
   * URLs are equivalent in terms of the context to which they refer.
   * Verification of whether the URLs are, or need to be, equivalent is up
   * to the context factory. The order of the URLs in the array is
   * not significant.
   * The object returned by getObjectInstance() is like that of the single
   * URL case.  It is the object named by the URLs.
   * <li>
   * If <code>obj</code> is of any other type, the behavior of
   * <tt>getObjectInstance()</tt> is determined by the context factory
   * implementation.
   * </ol>
   *
   * <p>
   * The <tt>name</tt> and <tt>environment</tt> parameters
   * are owned by the caller.
   * The implementation will not modify these objects or keep references
   * to them, although it may keep references to clones or copies.
   *
   * <p>
   * <b>Name and Context Parameters.</b> &nbsp;&nbsp;&nbsp;
   * <a name=NAMECTX></a>
   *
   * The <code>name</code> and <code>nameCtx</code> parameters may
   * optionally be used to specify the name of the object being created.
   * <code>name</code> is the name of the object, relative to context
   * <code>nameCtx</code>.
   * If there are several possible contexts from which the object
   * could be named -- as will often be the case -- it is up to
   * the caller to select one.  A good rule of thumb is to select the
   * "deepest" context available.
   * If <code>nameCtx</code> is null, <code>name</code> is relative
   * to the default initial context.  If no name is being specified, the
   * <code>name</code> parameter should be null.
   * If a factory uses <code>nameCtx</code> it should synchronize its use
   * against concurrent access, since context implementations are not
   * guaranteed to be thread-safe.
   * <p>
   *
   * @param obj The possibly null object containing location or reference information that can be
   * used in creating an object.
   * @param name The name of this object relative to <code>nameCtx</code>, or null if no name is
   * specified.
   * @param nameCtx The context relative to which the <code>name</code> parameter is specified, or
   * null if <code>name</code> is relative to the default initial context.
   * @param environment The possibly null environment that is used in creating the object.
   * @return The object created; null if an object cannot be created.
   * @throws Exception if this object factory encountered an exception while attempting to create an
   * object, and no other object factories are to be tried.
   * @see NamingManager#getObjectInstance
   * @see NamingManager#getURLContext
   */
  public Object getObjectInstance(Object obj, Name name, Context nameCtx,
      Hashtable<?, ?> environment)
      throws Exception;
}
